1. Field of the Invention
The present invention relates to a transmitter-receiver. More particularly, the present invention relates to a transmitter-receiver to which an external transmitter and receiver can be connected.
2. Background of the Invention
Although a portable telephone set has a transmitter and a receiver incorporated therein, there is a portable telephone with which an external transmitter and receiver, hereinafter briefly called "external transmitter-receiver", can be used.
FIG. 1 shows appearance of such a portable telephone 10, as well as an earphone-microphone 60 as an example of such an external transmitter-receiver, and FIG. 2 shows an example of circuit configuration of the portable telephone 10. Referring to FIG. 2, reference numeral 11 denotes a transmitter incorporated in the body, 13 denotes a transmitter circuit, 15 denotes a receiver circuit, 17 denotes a receiver incorporated in the body, and 19 denotes a connector jack to which a plug of a later described earphone-microphone is connected.
When speaking over the telephone, an audio signal from the transmitter 11 is supplied to the transmitter circuit 13 through a signal path of a switch contact C of the jack 19.fwdarw.an input contact D of the jack 19.fwdarw.an amplifier 12. The audio signal supplied to the transmitter circuit 13 is converted in the transmitter circuit 13 to a transmit signal for the up channel and the transmit signal is transmitted from a transmit/receive antenna 14 to a base station. A transmit signal transmitted from the base station over the down channel is received by the antenna 14 and supplied to the receiver circuit 15, in which an audio signal from the other party is extracted from the received transmit signal. The audio signal extracted by the receiver circuit 15 is supplied to the receiver 17 through a signal path of an amplifier 16.fwdarw.an output contact A of the jack 19.fwdarw.a switch contact B of the jack 19. Character E in the jack 19 denotes a grounded contact as the common contact. Conversation by telephone using a portable telephone can be achieved in the described manner.
Reference numeral 21 denotes a microcomputer for system control, 22 denotes a signal generator for generating a DTMF signal, a ringer sound signal, and the like, 24 denotes an incorporated speaker as a ringer, 25 denotes dial keys, and 26 denotes various control keys. The above described circuits are controlled by the microcomputer 21 and, thereby, sending a call, receiving a call, talking as described above, terminating a call, and the like are achieved.
Accordingly, the portable telephone 10 as a separated unit can be used in the same way as a general portable telephone is used. The transmitter 11, receiver 17, jack 19, antenna 14, dial keys 25, and control keys 26 are installed on the body of the telephone 10 as shown in FIG. 1, whereas the transmitter circuit 13, receiver circuit 15, and other circuits such as a power supply circuit are contained in the telephone body 10.
On the other hand, the earphone-microphone 60, as shown in FIG. 1, has an earphone 61 of an inner-ear type serving as a receiver and a microphone 62 serving as a transmitter. The earphone 61 and microphone 62 are connected to a connector plug 64 by a flexible connection cord 63. In this case, the earphone 61 is joined to the end of the cord 63. The microphone 62 is provided midway along the cord 63 approximately 13 to 15 (cm) apart from the earphone 61, i.e., where it can suitably collect the speech of the user when the user of the telephone 10 sets the earphone 61 to his ear, for example at the level around the mouth to throat. For an inner-ear type earphone, refer for example to U.S. Pat. No. 4,736,435.
When the plug 64 of the earphone-microphone 60 is inserted into the jack 19, the contacts C and D of the jack 19 are turned off and the microphone 62 of the earphone-microphone 60 is connected to the input contact D by the plug 64 as shown in FIG. 2. At the same time, the contacts A and B of the jack 19 are turned off and the earphone 61 of the earphone-microphone 60 is connected to the output contact A by the plug 64. As a result, the transmitter 11 and receiver 17 incorporated in the telephone are cut off from the amplifiers 12 and 16, respectively, but, instead, the microphone 62 and earphone 61 of the earphone-microphone 60 are connected to the amplifiers 12 and 16, respectively and thus conversation by telephone can be achieved using the earphone-microphone 60.
When the earphone 61 is set to the ear for example as shown in FIG. 3, it is not necessary to hold the transmitter-receiver while talking. Therefore, it is possible to keep the hands free while talking. When a call comes in while the user is walking, the user can receive the call by pushing a single key 26 of the portable telephone 10 and, hence, the telephone can be used more conveniently than when the transmitter 11 and receiver 17 of the portable telephone 10 are used.
As described above, the jack 19 is provided with mechanical switch contacts B and C and it should be arranged such that the contacts B and C separate from the contacts A and D, respectively to turn off when the plug 64 is inserted in the jack 19, while the contacts B and C contact the contacts A and D, respectively to turn on when the plug 64 is not inserted in the jack 19.
When the jack 19 is provided with such two switch contacts, the jack 19 becomes larger in size and this prevents realization of a small-sized telephone 10. Further, it places restrictions on wiring to the jack 19 or on the pattern of the printed board.
When the earphone-microphone 60 is connected to a portable telephone 10, the ringer sound announcing an incoming call is output only from the earphone 61 of the earphone-microphone 60. Therefore, when the user of the telephone 10 does not have the earphone 61 set to his ear, the ringer sound of the incoming call cannot be heard. When it is arranged such that the ringer sound is output only from the speaker 24 of the telephone 10, it may occur, when the earphone 61 is set to the ear, that the ringer sound of the incoming call is shielded by the earphone 61 and the incoming call is left unnoticed.
Therefore, when an earphone-microphone 60 is connected to a portable telephone 10, the ringer sound must be output from both of the earphone 61 of the earphone-microphone 60 and the speaker 24 of the telephone 10. However, the ringer sound output from the earphone 61 should be low enough not to adversely affect the sense of hearing. When the earphone-microphone 60 is not connected to the portable telephone 10, a ringer sound with a sufficient volume should be output from the speaker 24.
It is impossible to output the ringer sound with the above described volume by the use of the switch contact C of the jack 19. It is needed to provide a further contact in the jack 19 so that the path for supplying the ringer sound to the earphone 61 and the path for supplying the ringer sound to the speaker 24 are separated and properly adjusted ringer sounds are supplied through the paths.